Caijun Wang

Measurement of River Surface Currents With UHF FMCW Radar Systems

Three field experiments were conducted using a surface currents ultra-high frequency (UHF) radar system at fresh water during 2005. Two geometries for the transceiver antennas were examined: bistatic on a bank with an obstruction between them and backscatter on a bank. Echo Doppler spectra from a lake and two rivers were observed and interpreted. The first-order Bragg-echoes with Signal-to-Noise Ratios (SNR) of 20–50 dB were received and the maximum range was about 500 m with about 2∼3 w of transmitter power. Along-river surface currents have been measured using the UHF radar system. Comparisons with a conventional propeller-type current meter indicated that currents measured by UHF radar closely tracked in-situ current measurements.

Design and FPGA implementation of digital pulse compression for chirp radar based on CORDIC

The paper presents a full digitized approach for the pulse compression implementation in chirp radars. The emphasis is to cancel the quadratic phase term of the echo using a coordinate rotation digital computer (CORDIC). This approach has been implemented on a field programmable gates array (FPGA) and the compressed output peak is 100dB larger than the noise.

Wind Turbine Clutter Mitigation in Coastal UHF Radar

Coastal UHF radar provides a unique capability to measure the sea surface dynamic parameters and detect small moving targets, by exploiting the low energy loss of electromagnetic waves propagating along the salty and good conducting ocean surface. It could compensate the blind zone of HF surface wave radar at close range and reach further distance than microwave radars. However, its performance is susceptible to wind turbines which are usually installed on the shore. The size of a wind turbine is much larger than the wavelength of radio waves at UHF band, which results in large radar cross section. Furthermore, the rotation of blades adds time-varying Doppler frequency to the clutter and makes the suppression difficult. This paper proposes a mitigation method which is based on the specific periodicity of wind turbine clutter and performed mainly in the time-frequency domain. Field experimental data of a newly developed UHF radar are used to verify this method, and the results prove its effectiveness.

Phase-coded interrupted continuous waves analysis, parameters design and processor design

The paper presents the waveform analysis and parameters design involved with range resolution, maximum detect range, transmit interval and receive interval, in phase-code interrupted continuous wave (PCICW) radars. More attention is paid to the effect of transmit/receive gating. Range blinds are avoided by ensuring the pulse travels to and from the maximum detect range before the next pulse is emitted. It is shown that certain complementary sets with column orthogonality are adequate for our applications. Although the echo is partially suppressed by the gate, the compressed output retains zero range sidelobe performance. Simulation demonstrates that P4 codes are insentivity to Doppler effect in PCICW radars so it can simplify the receiver complexity, and the experiment shows that the sidelobes level are -90dB compared to the mainlobe.

Wind turbine clutter signature for maritime UHF radar

Scattering signal variability due to wind turbine blade rotation usually degrades the performance of nearby radio systems, which severely inhibits the development of wind power installation. As for the maritime ultra-high frequency (UHF) radar, the wind turbine clutter (WTC) may mask small targets and increase the error of sea state measurement. In order to solve the problem from the radar side, a complete understanding of the WTC signature is needed. Using the data of a 10-day in-field experiment on the coast of Fujian Province of China, this paper studies the empirical characteristics of WTC in maritime UHF radar from several signal processing domains, including the time, frequency, space, and polarization domains. Several methods for detection and mitigation of WTC are proposed which are based on the unique characteristics of WTC, such as the time-periodicity, frequency expansion, space concentration, and much stronger magnitude than the ocean-scattered signals when both the transmitting and receiving antennas are horizontally polarized.